Improvement of the mapping accuracy in material modelling with the integration of the yield locus at plane strain

• Applicant: Professorin Dr.-Ing. Marion Merklein
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 412137480

In many industries, there is a trend to reduce the overall weight of the product by the concept of lightweight construction. In the automotive industry, for example, this development is being further accelerated by legal requirements to reduce CO2 emissions. To achieve this, a central aspect is resource efficient production. Components made of conventional materials with a high sheet thickness are substituted by high strength materials with lower thickness or materials with a lower specific density and thus a reduced weight. The challenge in this context is the limited formability of these innovative materials. Especially the material behavior at plane strain is of decisive importance, since the lowest formability is present there and severe sheet thinning occurs even at a low deformation. As a result, more than 80% of the failures in deep drawing processes in automotive engineering are due to a state of plane strain or near plane strain. Therefore, it is necessary to investigate the material properties in the state of plane strain. Materials with a distortional hardening mechanism, such as deep-drawing steel of the DC grade, exhibit a hardening behavior that depends on the degree of deformation and the load path. For these materials, it is crucial to map the relevant deformation-dependent material properties with sufficient precision in the mathematical yield locus model. Conventional material models, which are available in commercial FE software, do not offer this degree of freedom. The primary goal of this research project is therefore the fundamental investigation of material hardening in the plane strain state and the influence of distortional hardening on the accuracy of the initial modelled yield locus. By means of sample processes, indicators are developed that enable an optimized parameter identification. Based on the material characterization at different strains and different load paths, yield loci are identified. By comparing the modelled and experimental yield stress, an error value can be calculated which allows a statement about the model quality. Furthermore, an analytical indicator is developed, which defines a degree of deformation based on the forming process, at which the parameter identification of the yield locus model leads to a maximum of mapping accuracy. The result is an increased knowledge about the material behavior at plane strain and, derived from this, the qualification of an optimized material modelling, with the lowest possible number of required material tests and thus an efficient material characterization.

• DFG Programme: Research Grants